The objective of this paper is to report new data for flow of gases, liquids, and liquid mixtures in 11 m long micro-channels. Three test sections of the following dimensions (a) 1.5 mm deep × 0.75 mm wide (MC1), (b) 0.5 mm deep × 0.95 mm wide (MC2), and (c) 0.3 mm. deep × 1.0 mm wide (MC3) were cut in a serpentine form on a stainless steel substrate. The gases studied were air, nitrogen, and oxygen. The liquids used were ethanol, methanol, and their mixtures. The measured flow rate and pressure drop were used to evaluate friction factors in the micro-channels. Analysis of friction factor versus Reynolds number relation shows a perceptible dependence on channel dimensions. Transitions to turbulent regime were identified by a change in slope of friction factor versus Reynolds number curve. Transitions were mild and occurred at lower Reynolds numbers than in normal channels. The results are interpreted in terms of a channel geometry parameter. © IMechE 2005.